Forging has been used to manufacture thin components such as aero-engine casings. The manufacture of engine casings from forgings is expensive in terms of material wastage and in machining time. Typically ninety five percent of the forged material is removed during the machining of aero-engine casings. This low material utilization is a consequence of including within the wall thickness of the forging, features such as bosses and the like. Bosses are common features on aero-engine casings since they are used extensively for mounting pipes and vane spigots.
As an alternative to using forgings it has been proposed that aero-engine casings should be manufactured from thin material, either roll forged or sheet material. Welding techniques are then used to attach bosses and other features to the thin material.
Attempts to inertia or friction weld bosses to structures manufactured from thin material have not been successful. The thin material cannot support the high loads generated during the friction welding process. This results in the boss punching through the thin material before a satisfactory weld is achieved.